The research proposed in this Phase Il application will result in a commercialized rapid test for bacterial contamination of platelets. The test is based on the identification in Phase I of novel peptidoglycan-binding peptides and proteins which react broadly with both gram-positive and gram-negative bacterial species. These reagents have been demonstrated to detect fewer than 104 bacterial cells/ml in a filtration assay with less than 30 minute turnaround time. In Phase II, the peptidoglycan-binding peptide reagents and assay format will be optimized and developed for commercial application in blood bank and hospital laboratories. Assay performance, sensitivity and specificity will be validated through clinical evaluations of the final product. The test will provide a cost-effective approach to pre-screening platelets for transfusion, and will potentially make possible an extension of the expiration date of platelet units beyond the current 5-day limit. At the same time, this fast and accurate test will increase the safety of platelet transfusion and thereby prevent serious or fatal transfusion-associated sepsis in transfusion recipients.